Respirator

ABSTRACT

A volume-limited general medical respirator is controlled by an integrated fluidic circuit. The respirator includes various alarm systems, control valving and main exhalation and inhalation phases operated entirely through gas means. A collapsible bellows is utilized to inspire the patient and is powered by an operative gas such as oxygen. The same operative gas not only powers the bellows during inspiration of the patient but is then recycled during the exhalation phase and thereafter used in the system for introduction to the patient during the subsequent inspiration phase.

United States Patent [191 Valenta et al.

[ Aug. 27, 1974 RESPIRATOR [75] Inventors: James D. Valenta, Madison; Ulrich Sielaff, McFarland, both of Wis; Stephen H. Drabkin, Woodbridge, Conn.

[73] Assignee: Airco, Inc., New York, NY.

[22] Filed: July 25, 1972 [21] Appl. No.: 275,019

[52] US. Cl. l28/ll45.8, 137/63 R [51] llnt. Cl A6lm 16/00 [58] Field of Search l28/l45.5, 145.6, 145.7,

[56] References Cited UNITED STATES PATENTS 3/1967 Andrcasen 128/1458 2/1973 Kipling 128/1458 OTHER PUBLICATIONS Automatic Ventilation of the Lungs, Mushin et a1. 1969, Chapter 11.

Automatic Ventilation of the Lungs, Mushin et al. 1969, pages 403-405.

Automatic Ventilation of the Lungs, Mushin et a1. 1969, Chapt. 54.

Primary ExaminerRichard A. Gaudet Assistant Examiner-G. F. Dunne Attorney, Agent, or Firm-Roger M. Rathbun; H. Hume Mathews; Edmund W. Bopp [57] ABSTRACT A volume-limited general medical respirator is controlled by an integrated fluidic circuit. The respirator includes various alarm systems, control valving and main exhalation and inhalation phases operated entirely through gas means. A collapsible bellows is utilized to inspire the patient and is powered by an operative gas such as oxygen. The same operative gas not only powers the bellows during inspiration of the patient but is then recycled during the exhalation phase and thereafter used in the system for introduction to the patient during the subsequent inspiration phase.

16 Claims, 4 Drawing Figures PAIENIEDnuczmn sum 10? 2 AIR //V 02 AND A/R M/XTURE OUT I64 0 AND AIR MIXTURE OUT FIG. 4

RESPIRATOR BACKGROUND OF THE INVENTION This invention relates to patient breathing equipment and more particularly to a volume limited respirator for assisting in the breathing or respiration of a patient.

Basically there are two types of medical respirators presently in use, one of which is a pressure limited respirator wherein the inspiration cycle is terminated when a predetermined pressure is sensed in the patient circuit. The predetermined sensed pressure indicates when the lungs are inflated at or near full capacity. A pressure limited respirator has a disadvantage in that the specific volume of gas delivered to the patient is generally uncertain and may vary during use of the respirator since the specific delivered volume is dependent upon the compliance of the patients lungs.

A volume-limited respirator on the other hand provides a given predetermined volume of gas to the patient and continues to provide this predetermined volume during the respirator use. The volume-limited respirator does not depend upon patient lung compliance but operates to deliver a specific known volume of gas to the patient during each inhalation cycle. A volumelimited respirator may also include a pressure relief means which is responsive to a predetermined pressure sensed in the patient circuit in order to activate an alarm or otherwise terminate the inhalation phase in case of a pressure build-up in the patient airways caused by a flow stoppage such as an obstruction in the patient circuit.

In the field of medical respirators it is an advantage to power the apparatus entirely from a gas source and thus eliminate any electrical components or electrical connections which can be hazardous in the presence of oxygen which readily supports combustion. In this manner only a single source of power is necessary for operating the entire apparatus and electrical hazards are eliminated.

ln hospitals a convenient source of pressurized supply is oxygen which is generally piped into various treatment or care rooms for easy access at many locations, however, the present respirator is operative with other gases under pressure, including air.

A medical respirator, in addition to other functions, must provide a varied range of oxygen concentrations to the patient and, preferably, an infinite range beginning at about 21 percent oxygen up to and including 100 percent oxygen. Any setting within this range must remain stable throughout the respirator operation. such oxygen ranges are normally provided on present respirators through a plurality of orifices which are changed to alter the oxygen concentration and, generally, the mixing between oxygen and air to vary oxygen concentrations occurs at relatively elevated pressures above atmospheric pressure.

SUMMARY OF THE INVENTION In the present invention there is provided a fluidically controlled respirator for general medical use which is or controls are commercially available and may be devised by suppliers to meet whatever necessary design parameters are determined for the respirator.

An oxygen mixing system is used in the present respirator and includes a variable area relationship between incoming oxygen at approximately atmospheric pressure and make-up air at atmospheric pressure, which allows an infinite control through the entire selectable range and provides a stable oxygen/air volume output throughout the use of the respirator.

The oxygen source powers a collapsible bellows for inhalation of the patient with gas contained within the bellows. The same operative gas used to power the bellows is thereafter channeled through an oxygen mixing system and delivered to the interior of the bellows in a predetermined oxygen concentration to be supplied to the patient during the next inhalation phase. In this manner the most advantageous use is made of the pressurized oxygen since it is not only used to power or collapse the bellows but is therafter cycled, proportioned with air and introduced to the patient.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic illustration of the respirator circuitry used with the present invention.

FIG. 2 is a side elevational view of an oxygen mixing valve used on the respirator of this invention.

FIG. 3 is a cross-sectional view of the oxygen mixing valve taken along the line 33 of FIG. 2.

FIG. 4 is a plan view of the oxygen mixing valve.

DESCRIPTION OF THE INVENTION A. Basic Flow Circuit Referring to FIG. 1, there is shown a schematic of the overall respirator system having a main conduit means 22 which is adapted to be connected at 20 to a source of oxygen under a pressure of about 50 psi. A main control valve 24 in the conduit 22 controls the supply of oxygen to the respirator. A normally closed interface valve 26 is also interposed in main supply conduit 22 and operates to control the supply oxygen to a venturi 28 through duct 30. The operation of the interface valve 26 alternates between an opened and a closed position under certain conditions which will be later explained.

A portion of the supply oxygen is bled from main conduit 22 intermediate the main control valve 24 and interface valve 26, through bleed duct 32 into a regulator 34. The regulator 34 serves to reduce the supply oxygen pressure to approximately 3 psi. for operation of the integrated fluidic circuit, shown as block diagram 36. A filter 38 removes any impurities in bleed duct 32 to insure that the gas reaching the fluidic circuit 36 is free from harmful particles which might adversely affect its control characteristics. In the event an undue quantity of particles is built up within the filter 38, causing the output pressure from the filter 38 to be reduced a predetermined amount, a feed-back line 40 senses a predetermined reduction in pressure and signals the regulator 34 to open a corresponding amount to offset the decreased sensed pressure. In this manner, even though filter 38 becomes partially clogged or otherwise obstructed, a relatively constant signal pressure is assured for operating the fluidic circuit 36.

The oxygen supply from interface valve 26, when open, enters venturi 28 and its flow through the venturi 28 is controlled by a control duct 42 having a venturi flow control valve 44 in the flow stream. The control duct 42 communicates with the throat-of the venturi and by controlling the flow in control duct 42, the flow through the venturi 28 can be correspondingly controlled.

The venturi 28, itself, is disposed within the entrance to a venturi chamber 46. An open passageway 48 provides communication between the venturi chamber 46 and the interior of a bellows container 50. A bellows 52 is freely suspended within the bellows container 50 and is circumferentially sealed to the upper surface of container 50. A further opening in the bellows container 50 is formed in the bottom thereof and is controlled by an inflatable mushroom valve 54. The interior of bellows 52 is isolated from the remaining interior of the bellows container 50, such that an inhalation of the patient, the pressure in the bellows container 50 is raised in order to collapse the bellows 52, thereby expelling any gas within the bellows 52 through patient conduit 56 to the patient, shown as 58. Within the patient conduit 56, there is also located a check valve 60 to prevent the patients exhaled breath from being reintroduced into the bellows. A filter 62 removes any impurities in the form of pathogens which might be present within the gas from the bellows 52, and a humidifier 64 may be provided to add moisture to the gas to be inhaled by the patient. A patient exhaust valve 66 is teed from patient conduit 56 and opens the patient conduit 56 to the surrounding atmosphere during the exhalation phase, thereby forming a short path for the patients exhalation.

During the inhalation and exhalation cycles, which will be later explained, the bellows 52, after reaching its uppermost position, is allowed to drop by means of gravity. A weight is normally located in the bottom of the bellows 52 to hasten its downward travel. As the bellows 52 drops, the gas which had filled the bellows container 50, exterior of bellows 52, is exhausted through mushroom valve 54 and enters an oxygen mixer 68 through conduit 70. A further flow of gas from the bellows container 50 is caused to pass downwardly through passageway 48 and into the venturi chamber 46. A pop-off valve 102 is in communication with the interior of the venturi chamber 46 at a point 103 upstream of the venturi 28. This valve 102 is held closed whenever gas from duct 30 is flowing through the venturi 28, since a slight vacuum is drawn at 103. When gas is exhausted from bellows 52 as described, however, the venturi 28 is not being used, therefore, the increase in pressure in venturi chamber 46 caused by the exhausted gas, opens pop-off valve 102 and allows the gas to combine, in conduit 70, with that gas which has exhausted through the mushroom valve 54. A standpipe conduit 72 connects the conduit70 to atmosphere and serves to reduce the pressure of gas entering the oxygen mixer 68 from conduit 70 to at or slightly above atmospheric pressure. The gas passing through conduit 70 is preferably oxygen which previously had been used to collapse bellows 52. In the oxygen mixer, the oxygen from conduit 70 is mixed with room air which enters the mixer 68 from conduit 74 and an-external filter 76. The oxygen mixer 68 will be fully explained further, however, it mixes the oxygen and air to a predetermined proportion and the mixed gas exits from the oxygen mixer 68 through conduit 78, check valve 80 and is introduced to the interior of the bellows 52 as the bellows descends downwardly in bellows container 50. In this manner the driving gas, oxygen, which forces the bellows to collapse on one phase of the cycle, is, on the very next cycle, exhausted, mixed to a predetermined proportion with room air and is introduced to the interior of the bellows 52, thereby utilizing a portion of the same oxygen for a powering gas and for the source of oxygen for introduction into the patient. When the respirator is set to operate on 21 percent oxygen, as will be later explained, all of the oxygen from the bellows container 50 is dumped to atmosphere through the standpipe conduit 72, and only room air is drawn into the bellows 52 through the oxygen mixer 68 as the bellows 52 descends downwardly. As it may be seen, and will be more fully explained in dealing with the control elements of this respirator, the oxygen/air mixture which enters the interior of bellows 52 from the oxygen mixer 68, is, on the succeeding phase, forced out of the bellows 52 as it is collapsed and thereafter enters the patient conduit 56 into the patient.

B. Inhalation Phase Control To better understand the various fluidic controls, the operation of the respirator is presented by referring to the two main phases of operation, the inhalation phase where gas is forcibly caused to enter the patient, and the exhalation phase where the patient is allowed to exhale gases from his lungs to the surrounding atmosphere.

The integrated fluidic circuit 36, used with the present respirator, is preferably a commercially designed unit employing fluidic amplifiers. Such fluidic circuits are generally analagous to present electrical components and can be designed fairly readily to perform almost any functions or provide any signals that heretofore have relied upon electrical devices. As such, therefore, the assembly or internal operation of the fluidic circuit itself does not form a part of the present invention but it is only shown and described in block form using its output and input ports as a black box type of operation. The fluidic circuit, therefore, will be explained in terms of the outputs and inputs utilized to control the various features which make up the present invention. The fluidic circuit itself is designed commercially to operate in the disclosed manner based on the desired parameters required by the particular respirator functions.

The respirator is operated by turning the main control valve 24 to the on position, thus allowing oxygen at about 50 p.s.i. from the supply 20 to be supplied to interface valve 26 and also to provide the powering gas to integrated fluidic circuit 36, the latter gas being reduced to a pressure of about 3 p.s.i. through regulator 34. When the respirator initiates its inhalation phase, either manually, automatically, or by patient triggering as will be later explained, a control signal appears at both Port B and Port E of fluidic circuit 36. These signals are indicated by the directional arrows appearing adjacent these control ports on FIG. 1.

The presence of a control signal at Port B is transmitted through control flow line 82 to interface valve 26, causing it to open. The interface valve 26 is shown as a typical commercially available pneumatic valve, however, a fluidic amplifier may be suitably operable by a control pressure. The interface valve 26 has an enclosed chamber 83 and a flexible diaphragm 85 which is displaced when a pressure signal is received within the enclosed chamber 83. A sufficient displacement of the flexible diaphragm 85 causes the valve operator 87 to move from the normally closed position as shown in FIG. 1, to an open position where a fluid passageway 89 within operator 87 is aligned with input port 91 and output port 93, thus allowing the 50 psi. supply oxygen to pass through the interface valve 26 into the venturi chamber 46. As previously explained, the flow into venturi chamber 46 is controlled by the flow control valve 44 which affects the flow through the venturi 28.

The increased pressure in the venturi chamber 46 is directly transmitted to the bellows container 50 through open passageway 48 and also serves to inflate, or close, the mushroom valve 54 through duct 84. The closed position of mushroom valve 54 is shown in the dotted line position in FIG. 1. The mushroom valve 54, when closed, prevents the flow of gas from the bellows container 50, thus allowing an immediate buildup of pressure within bellows container 50.

The increased pressure within bellows container 50 causes the bellows 52 to collapse, forcing the gas contained therein out through the patient conduit 56, check valve 60, patient filter 62, humidifier 64 and to the patient 58 through a mask, tracheal or endotracheal tube. The gas from the bellows 52 is prevented from being exhausted through conduit 78 by means of the check valve 80.

The exhaust valve 66 is closed, as indicated in the dotted line position on FIG. 1, so that the gas from bellows 52 is not exhausted to the surrounding room. Closing of exhaust valve 66 during the inhalation cycle is caused by the control signal appearing at Port E during the inhalation phase and which is transmitted via conduit 104 to a diaphragm control amplifier 86. A stretched diaphragm 88 within control amplifier 86 is displaced by the signal pressure to close a bleed opening 90 which, when open, normally allows the 3 psi. control oxygen signal from bleed conduit 92 and conduit 94, to be vented through openings 96 to the atmosphere. By closing the bleed opening 90, approximately 1.5 p.s.i. oxygen enters conduit 98 to the exhaust valve 66 and fills an expansible mushroom chamber to close exhaust valve 66. Again, although a diaphragm activated valve is shown schematically in FIG. 1, the diaphragm control amplifier 86 may be of comparable fluidic amplifier devices without departing from the spirit of this invention.

C. Exhalation Cycle Under normal operating conditions the shift from the inhalation phase to exhalation phases occurs when a predetermined volume of gas has been expelled from the bellows 52 to the patient, thus, the volume-limited respirator delivers a constant gas volume during each inhalation phase. The volume of gas admitted to the pa tient is determined by adjusting the stroke of the bellows 52 to a preset point by means such as a cord 100 extending down into the interior of the bellows fastened to the bottom thereof and having a windable spool 101 to adjust the length of cord 100. The cord 100 terminates the downward travel of the bellows when'its extended length has been reached. Once the length of the cord is set in accordance with the tidal volume desired for the patient, the respirator will continue to provide that volume throughout its normal operation each time the bellows is collapsed. At the uppennost point of the bellows stroke, a bellows switch 1 12 is closed. The bellows switch 112 comprises a magnet 113 having its poles coaxially positioned with respect to the movement of bellows 52 and vent holes 119. At the lower extremity of the bellows 52 is a magnet 1 15 having a predetermined pole position such that as the bellows reaches its uppermost position, a like pole of magnet 113 reacts with a like pole of magnet 115, causing the magnet 113 to be repelled upwardly, closing normally open duct 114 which, in the normally open position, vents through holes 119. This causes a signal to traverse through duct 1 14 to Port D of the fluidic circuit 36. When Port D receives a signal of at least a predetermined strength, it changes the mode of the fluidic circuit- 36 from its inhalation phase to its exhalation phase, and both Port B and Port E lose their con trol signals.

As Port B loses its signal, the interface valve 26 closes, thus shutting off the supply of oxygen to the venturi chamber 46 and the bellows container 50. As the pressure drops in venturi chamber 46, the inflated mushroom valve 54 becomes deflated and opens, as shown in the solid line position of FIG. 1, to allow gas within the bellows container 50 to pass into conduit 70. The pressure within the bellows container 50 is thereby depleted, allowing the bellows 5.2 to fall due to the force of gravity. As the bellows 52 drops, the oxygen within the surrounding bellows container is forced through the mushroom valve 54 into conduit and also through passageway 48, venturi chamber 46 and through pop-off valve 102 into conduit 70 for introduction into the oxygen mixer 68. The stand pipe conduit 72 lowers the pressure of this oxygen to, at or slightly above atmospheric pressure as it enters oxygen mixer 68. Also, since the stand pipe conduit 72 becomes filled with oxygen which is heavier than air, outside air does not enter the stand pipe conduit 72 to the oxygen mixer 68. In the alternative, a check valve may be located within stand pipe conduit 72 to prevent the entrance of outside air. Room air, at atmospheric pressure, is drawn into the oxygen mixer 68 through external filter 76 and conduit 74.

In FIGS. 2-4 there is shown an oxygen mixer which can be used in the present respirator and which proportions the air and oxygen by varying the area of the inlet openings for oxygen and air, however, the total opening, i.e. the total area of both openings remains constant, thus the total flow is constant despite a relative change in the air/oxygen concentration.

The principle of operation of the oxygen mixer 68, that of mixing the gases in proportion to the area of their respective inlets, while maintaining the total area of both inlets constant, may be physically accomplished in many devices, however, in FIGS. 2-4 the device therein shown has been found to produce good reliable mixing resultsin an economically attractive unit.

The oxygen mixer 68 comprises an oxygen inlet port 164 and an air inlet port 166 adapted to be connected, respectively, to conduits 70 and 74 shown in FIG. 1. The oxygen and air streams which enter their respective ports are at approximately atmospheric pressure and meet intermediate their inlet ports as will be described. The mixed stream of air/oxygen leaves the oxygen mixer 68 through discharge port 168 into conduit 78. An inwardly directed projection 170 within the dis charge port 168 serves to provide a fixed, reproducible orifice or circular area 171 through which the total flow of air/oxygen passes. A movable bafile 172 proportions the respective areas through which the air and oxygen streams pass through opening 171. A shown, the movable baffle 172 has a projection 174 which directs the respective air and oxygen streams into the discharge port 168. The projection 174 divides the area within the discharge opening 171 into two separate definable areas, indicated in FIG. 3 as areas A, and A Oxygen which enters the oxygen mixer 68 through inlet port 164 is channeled through the area designated as A while the room air entering through inlet port 166 is channeled through the area designated as A It may be seen, therefore, that by varying the proportions of A and A while maintaining the total of A, plus A constant, the relative mixture of air and oxygen can be controlled while the total flow remains constant. A change in the A,/A areas proportions is accomplished by moving baffle 172, thereby increasing or decreasing, simultaneously, the individual areas A, and A while maintaining the overall discharge opening 171 constant. A control shaft 174 is engaged with the movable baffle 172 by means of a threaded enlarged end 176 coacting with internally threaded bore 178 within movabe bafi'le 172. The shaft 174 is affixed to the oxygen mixer housing 180 through housing bore 182 and shaft retainers 184 and 186. The shaft retainer 184 and 186 prevent axial movement of the shaft 174 with respect to housing 180 while allowing rotational movement therebetween. A shaft seal 188 prevents the leakage of gas along the shaft 174. As the shaft 174 is rotated, therefore, the movable baffle 172, constrained against rotational movement by means such as a pin 190 retained within an elongated slot in the housing 180, is caused to move axially with respect to shaft 174, thereby adjusting the relative areas A, and A As an example of the operation of the oxygen mixer 68, in FIG. 3, the movable baffle 172 is shown in a position such that A, is about equal to A therefore, 50 percent air and 50 percent oxygen will be drawn through the oxygen mixer 68 and be discharged through port 168. If the movable baffle 172 is adjusted such that A, is zero, i.e., at the extreme right position of FIG. 3, no air will be admitted and 100 percent oxygen will be discharged through port 168. Similarly, if A, is zero, then all of the oxygen from the bellows container 50 is discharged through standpipe conduit 72 to room atmosphere, and only air (21 percent oxygen) is drawn through the oxygen mixer 68 to the interior of bellows 52. As it may readily be seen, the movable baffle 172 may be set at any desired intermediate position to provide between 2l percent oxygen and 100 percent oxygen. The mixing occurs at low pressure, at or near atmospheric, so that a predictable, fairly non-critical setting will retain the desired concentration with great stability.

Returning to FIG. 1, the oxygen/air mixture leaves the oxygen mixer 68 through conduit 78, check valve 80 and enters the interior of bellows 52 as the bellows 52 travels downward. The oxygen mixing is effected both by a slight position pressure in conduit 70 as a result of the belows 52 pushing oxygen from the bellows container 50, and also through a slight negative pressure in conduit 78 caused by the expansion of the interior of bellows 52 as it falls downwardly.

The oxygen mixing system conserves the use of oxygen since, during inhalation, the oxygen is the propelling force to collapse the bellows and the same propelling oxygen is then mixed with room air and used to fill the expanding bellows 52 during the exhalation cycle.

As the bellows 52 drops, the patient exhales through exhaust valve 66 to the outside atmosphere. Since, at the commencement of this exhalation phase, the signal at Port E has been lost by activation of bellows switch 112, the diaphragm 88 of control amplifier 86 returns to the position shown by solid lines in FIG. 1, thereby opening bleed passage 90 to atmosphere through opening 96. This allows a rapid deflation of the exhaust valve 66 to the position shown by solid line representation in FIG. 1, so that the patient may exhale to the room through the exhaust valve 66 via openings 117.

The bellows 52, on exhalation, reaches the lowermost point of its stroke fairly rapidly and is unaffected by the time period of the patients exhalation. The time of the exhalation phase, i.e., the period from the end of any one inhalation phase to the start of the next inhalation phase, is controlled by an adjustable orifice valve 118 which joins Ports K and L of the fluidic circuit 36. The adjustable orifice valve 1 18 essentially controls the period of the exhalation phase by varying the time in which a contained volume is filled within fluidic circuit 36. When the contained volume reaches a specified pressure, the fluidic circuit 36 changes to the inhalation phase. Therefore, by controlling the rate at which the contained volume is filled, the switchover time from the exhalation phase to the inhalation phase may be accurately adjusted.

A manual switchover from exhalation phase to inhalation phase is provided by pushbutton valve 120. The valve 120, when depressed, automatically switches the respirator into the inhalation phase no matter what phase the respirator is in at that time. The valve 120, if held depressed, will retain the respirator in the inhalation phase, thereby holding a full breath within the patient for the taking of X-rays or other tests. In this manner the attending hospital personnel can manually operate the respirator.

When switchover from exhalation to inhalation occurs, whether manually or by the expiration timing circuit, the fluidic circuit 36 again provides a signal at each of Ports B and E, thereby beginning the inhalation phase again.

The inhalation phase may also be initiated through an effort by the patient to inhale. A patient triggering bleed duct 122 extends from the patient conduit 56 to Port A of the fluidic circuit 36. A negative pressure of at least a predetermined threshold amount, such as occasioned by the patient attempting to inhale, signals Port A and causes the fluidic circuit 36 to switch over to the inhalation phase. In this manner, when the patient triggering feature is being used, the patient may operate the switchover from exhalation to inhalation, however, should the patient not signal the fluidic circuit 36, normal phase switchover will occur due to the timing circuit. The amount of negative pressure re-' quired by the patient to trigger the fluidic circuit 36 is adjustable by means of valve 119.

A pressure gauge 126 may be provided in communication with bleed duct 122 for a visual monitor of the inhalation pressure being applied to the patient, and also to provide a visual indication in the event a high pressure is built up in the patient conduit 56 as would be experienced in case of an obstruction in the path to the patients lungs.

A further visual monitor of the respirator is a patient trigger indicator 128 which is connected to Port l-l via duct 130. When Port A receives a negative signal sufficient to cause a switchover from exhalation to inhalation, a visual signal appears at the patient trigger indicator 12% so that hospital personnel can easily determine when the respirator is being cycled through patient effort. The patient trigger indicator 128 is a pressure operated device, commercially available, and re ceives a pressure signal to move a disc to a position where a bright color appears in a transparent window.

D. Alarm Circuits 1. Low Pressure Alarm An alarm is provided to sense a low pressure, or lack of pressure build-up in the patient conduit 56. This low pressure might occur if the patient breathing mask, tracheal or endotracheal tube, becomes dislodged from the patient so that the back pressure normally provided by the patients lungs during inhalation is not present.

This alarm is activated through Port C of the fluidic circuit 36, that Port being connected to the patient bleed duct 122 through duct 132 and senses the pressure which is provided to the patient. Port C is adapted, through the fluidic circuit 36, to require a signal of a predetermined pressure within a predetermined time interval or it will signal Port G that a low pressure or loss of pressure has occurred. In the preferred embodiment, Port C must receive a signal of about 8 cm. water at least every 15 seconds or it will cause a signal to appear at Port G. By this, the patient must be receiving gas at the rate of approximately four breaths per minute for which a predetermined back pressure is sensed at therefore, C. If, therefire, the connection means becomes dislodged from the patient, such that no back pressure is built up in patient conduit 56, a maximum of 15 seconds will pass before a signal will appear at Port G.

A signal appearing at Port G immediately activates the low pressure alarm indicator 134 through duct 136. The low pressure alarm indicator 134 is similar to the patient trigger indicator 123 and flashes a visual indication which is pressure activated.

In addition to this visual indicator 134, an audible alarm 138 may give a further alarm to attending personnel. The audible alarm 138 is operated by oxygen via conduit 92 at control pressure through diaphragm amplifier 140. Under normal conditions, the oxygen supply enters diaphragm amplifier 141) from conduit 92 and is vented to atmosphere through a bleed opening 142 and further openings 144. The bleed opening 142 may be closed by diaphragm 146 as shown in the dotted line position of FIG. 1 when an alarm condition is in effect, thereby channeling the oxygen directly through duct 148 to sound the audible alarm 138.

Movement of diaphragm 146 to close bleed opening 142 is effected by the signal which appears at Port G through duct 150 having a check valve 152 therein, and through duct 154. A toggle valve 156 in duct 1154 allows the attending personnel to connect or disconnect the operation of the audible alarm 138.

Once the low pressure condition has been rectified, Port C will again'receive a signal to indicate that back pressure in the patient circuit 56 has been restored. Port C will then disconnect the signal at Port G and will return to its normal function of determining that a signal in the patient conduit 56 is sensed every 15 seconds.

As the signal at Port G is removed, the low pressure alarm indicator 134 will return to its normal non-alarm status and the signal pressure in ducts 152 and 154 is removed, whereby diaphragm 146 is moved away from bleed opening 142, allowing the pressure within duct 148 and the audible alarm to be dumped to the atmosphere through openings 144 in diaphragm amplifier 140, silencing the audible alarm.

2. Failure to Cycle Alarm An alarm is provided in the event the respirator fails to operate during inhalation or during exhalation cycles.

a. Failure to Cycle Inhalation During the inhalation cycle, there is always a signal present at Port B since it controls the interface valve 26 which allows the oxygen to collapse bellows 52. Since inhalation can only occur when Port B is on, a timing device in the form of a contained volume within the fluidic circuit 36 is caused to fill. This volume is set to cause a signal to appear at Port F in the event that the signal at Port B is present beyond a predetermined time. As an example, if a signal is present at Port B for five seconds, or longer the contained volume reaches its predetermined pressure and a signal will appear at Port F. This would occur in the event an excessive pressure is built up within the patient such that the bellows would fail to collapse, thus the inhalation phase would, unless otherwise controlled, be continued indefinitely.

As the 5 second time interval is exceeded, a signal appears at Port F and also, the signal which would normally be present at Port E during inhalation is removed, thus the quick diaphragm valve 86 opens to relieve the pressure in the exhuast valve 66, thereby opening the patient circuit 56 to atmosphere. In this manner, the excess pressure which has been built up within the patient is allowed to vent to the room atmosphere.

The alarm signal that appears at Port F causes a recognition color to flash in the failure to cycle alarm indicator through duct 162. In addition, the audible alarm 138 is signalled in the same manner as described in connection with the low pressure alarm indicator 134. A check valve 153 is included in duct 154.

b. Failure to Cycle Exhalation This alarm operates from Port D since this Port is signalled whenever the bellows 52 reaches the top of its stroke to activate bellows switch 112 to change the fluidic circuit 36 from an inhalation phase to exhalation phase. If Port D does not receive a signal in a predetermined interval, such as 15 seconds, a signal is caused to appear at Port F.

In addition to causing a signal to appear at Port F, this alarm circuit also insures that the signal at Port E is off, thus insuring that diaphragm valve 86 is open to allow the patient to freely exhale to atmosphere through patient exhaust valve 66.

Therefore, in the event of any of the abnormal conditions under which an alarm might be triggered, i.e., low pressure, failure to cycle inhalation, or failure to cycle exhalation, the patient is immediately vented to the atmosphere through the exhaust valve 66, insuring patient safety.

We claim:

1. A respirator adapted to be connected to a source of first gas under pressure, said respirator comprising a bellows container and an expandable, collapsible bellows operatively positioned within said bellows container, valve means for introducing the first gas into said bellows container to collapse said bellows, an inhalation conduit for receiving gas from said bellows whereby said bellows delivers a predetermined volume of a portion of the first gas to patient, means to remove the first gas from said bellows container during expansion of said bellows, means for reducing the pressure of said removed gas to substantially atmospheric pressure, mixing means for combining at least a portion of the first gas removed from said bellows container with a second gas at substantially atmospheric pressure and means to introduce the mixed first and second gases into said bellows during expansion of said bellows for delivery to said inhalation conduit during subsequent collapse of said bellows.

2. A respirator as defined in claim 1 wherein said first gas is oxygen and the second gas is air.

3. A respirator as defined in claim 1 wherein said mixing means comprises a chamber at about atmospheric pressure.

4. A respirator as defined in claim 3 wherein said chamber has a first and second valve means for introducing said first and second gases to said chamber, said first and second valve means having variable size openings wherein the total opening area of said first and second valve means is constant.

5. A respirator in accordance with claim 1, wherein said valve means for introducing said first gas into said bellows container includes a venturi chamber having an outlet to said bellows container, a first inlet branch for delivering said gas to said venturi chamber upstream of a ventui formed therein, and a second adjustably valved inlet branch in parallel with said first branch and delivering gas to the reduced pressure zone at said venturi in accordance with the preset adjustment of said valve; said adjustment by regulating the flow of said first gas into said container varying the rate of collapse of said bellows.

6. A respirator system comprising in combination:

a bellows container having an inlet and a valved outlet port;

a bellows mounted in said container, said bellows having an inlet and an outlet, and being expandable to a predetermined volume;

gas conduit means communicating said container outlet port to said bellows inlet;

a breathing circuit connected to said bellows outlet;

a source of first gas under pressure;

first control means operable to connect said first gas to said container inlet while closing said container outlet port to pressurize said container, thereby collapsing said bellows and delivering the predetermined volume of gas to said bellows outlet;

second control means operable upon said bellows reaching its collapsed condition to open said container outlet port to remove the first gas from said bellows container;

means for reducing the pressure of said removed gas to substantially atmospheric pressure;

mixing means for combining at least a portion of the first gas removed from said bellows container with a second gas at substantially atmospheric pressure; and

means to introduce the mixed gases into said bellows during expansion of said bellows for delivery to said breathing circuit during subsequent collapse of said bellows.

7. Apparatus according to claim 6 wherein said second control means includes a gas pressure switch mounted externally to said container; said switch comprising a normally-bled orifice and a valve body displaceable into said orifice to close said orifice; said valve body carrying a first magnetic pole; the extensible end of said bellows carrying a second magnetic pole of the same polarity as said first pole; said first magnetic pole being responsive to the repellent force with said second magnetic pole when said bellows moves to its collapsed condition to drive said valve body into said orifice to close said orifice, the closing of said orifice providing a pressure signal for actuating said second control means.

8. A medical respirator system, comprising in combination:

a. a source of gas pressure;

b. a bellows container having an inlet and a valved outlet controlled by a pressure chamber;

c. a bellows having an inlet and an outlet mounted within said container, said bellows being expandable and collapsible between end positions;

d. said source of fluid pressure being connected to said container through an interface valve and said pressure chamber;

e. a breathing circuit for a patient serviced by said system being connected to the outlet of said bellows volume, said breathing circuit including exhaust valve means for venting said breathing circuit;

f. control means for said breathing circuit exhaust valve;

g. said valved outlet of said bellows container being connected to the inlet of said bellows; and

h. fluid logic circuit means connected to said pressure source, to said control means for said breathing circuit exhaust valve, and to said interface valve; said circuit means being adapted to: l provide a first enabling signal for opening said interface valve to pressurize said chamber, thereby closing said container outlet valve and pressurizing said container to collapse said bellows forcing gas into said breathing circuit; (2) provide to said breathing circuit exhaust valve control means a second enabling signal simultaneous with said first enabling signal, for maintaining said breathing circuit exhaust valve closed; (3) terminate said first and second enabling signals to close said interface valve upon said bellows reaching its collapsed end condition, thereby removing pressure from said chamber and opening said outlet valve of said container enabling flow of gas from said container to said bellows inlet to expand said bellows, while opening said breathing circuit exhaust valve to relieve said breathing circuit pressure.

9. A system in accordance with claim 8, including fluid switch means connected to said fluid logic circuit means, said switch means being operable upon said bellows reaching its collapsed end condition to provide a signal to said logic circuit for terminating said first and second enabling signals to said interface valve and breathing circuit exhaust valve control means.

10. A system in accordance with claim 9, wherein said switch means includes a normally bled orifice, and a valve body displaceable to close said orifice, both said elements being mounted external to said container; said valve body including at least a first magnetic pole adjacent said container; and wherein the movable end of said bellows carries magnet means having a second pole opposite to the polarity of said first pole, movement of said bellows to said second position bringing said second pole toward said first pole to drive said valve body toward said orifice, thereby closing said orifice and providing said signal to said logic circuit.

111. A system in accordance with claim 10, further including means coupling the pressure in said breathing circuit to an alarm input port at said fluid logic circuit, said logic circuit being adapted to provide at a first alarm output a first alarm signal upon the pressure at said breathing circuit dropping below a first predetermined level; and visual alarm indicator means connected to said first alarm signal to provide visual indication means connected to said first alarm signal to provide visual indication of said alarm condition.

12. A system in accordance with claim 11, further including audible alarm indicator means coupled to said pressure source through a control valve means; said first alarm signal being coupled to said control valve whereby occurrence of said signal activates said control valve to enable said audible alarm.

13. A system in accordance with claim 11, wherein said fluid logic circuit includes a second alarm output, timing means at said fluid logic circuit being adapted to provide a second alarm signal at said second output when the first enabling signal to said interface valve is present beyond a predetermined time period, said second signal being coupled to alarm indicators thereby signalling failure of cycling in said respirator system.

14. A system according to claim 13, wherein said first and second alarm signals are both connected to a common alarm indicator.

15. A system in accordance with claim 11, wherein the said fluid logic circuit is further adapted to terminate said first and second enabling signals upon the pressure from the said breathing circuit dropping below a second predetermined level, whereby said system is triggered between inhalation and exhalation phases in consequence of patient breathing effort.

16. A system in accordance with claim 15, wherein said fluid logic circuit is adapted to provide a patient trigger signal upon said system being switched between said inhalation and exhalation phases by said patient effort, said signal being coupled to an observable alarm indicator means to indicate said patient triggered condition. 

1. A rEspirator adapted to be connected to a source of first gas under pressure, said respirator comprising a bellows container and an expandable, collapsible bellows operatively positioned within said bellows container, valve means for introducing the first gas into said bellows container to collapse said bellows, an inhalation conduit for receiving gas from said bellows whereby said bellows delivers a predetermined volume of a portion of the first gas to patient, means to remove the first gas from said bellows container during expansion of said bellows, means for reducing the pressure of said removed gas to substantially atmospheric pressure, mixing means for combining at least a portion of the first gas removed from said bellows container with a second gas at substantially atmospheric pressure and means to introduce the mixed first and second gases into said bellows during expansion of said bellows for delivery to said inhalation conduit during subsequent collapse of said bellows.
 2. A respirator as defined in claim 1 wherein said first gas is oxygen and the second gas is air.
 3. A respirator as defined in claim 1 wherein said mixing means comprises a chamber at about atmospheric pressure.
 4. A respirator as defined in claim 3 wherein said chamber has a first and second valve means for introducing said first and second gases to said chamber, said first and second valve means having variable size openings wherein the total opening area of said first and second valve means is constant.
 5. A respirator in accordance with claim 1, wherein said valve means for introducing said first gas into said bellows container includes a venturi chamber having an outlet to said bellows container, a first inlet branch for delivering said gas to said venturi chamber upstream of a ventui formed therein, and a second adjustably valved inlet branch in parallel with said first branch and delivering gas to the reduced pressure zone at said venturi in accordance with the preset adjustment of said valve; said adjustment by regulating the flow of said first gas into said container varying the rate of collapse of said bellows.
 6. A respirator system comprising in combination: a bellows container having an inlet and a valved outlet port; a bellows mounted in said container, said bellows having an inlet and an outlet, and being expandable to a predetermined volume; gas conduit means communicating said container outlet port to said bellows inlet; a breathing circuit connected to said bellows outlet; a source of first gas under pressure; first control means operable to connect said first gas to said container inlet while closing said container outlet port to pressurize said container, thereby collapsing said bellows and delivering the predetermined volume of gas to said bellows outlet; second control means operable upon said bellows reaching its collapsed condition to open said container outlet port to remove the first gas from said bellows container; means for reducing the pressure of said removed gas to substantially atmospheric pressure; mixing means for combining at least a portion of the first gas removed from said bellows container with a second gas at substantially atmospheric pressure; and means to introduce the mixed gases into said bellows during expansion of said bellows for delivery to said breathing circuit during subsequent collapse of said bellows.
 7. Apparatus according to claim 6 wherein said second control means includes a gas pressure switch mounted externally to said container; said switch comprising a normally-bled orifice and a valve body displaceable into said orifice to close said orifice; said valve body carrying a first magnetic pole; the extensible end of said bellows carrying a second magnetic pole of the same polarity as said first pole; said first magnetic pole being responsive to the repellent force with said second magnetic pole when said bellows moves to its collapsed condition to drive said valve body into said orifiCe to close said orifice, the closing of said orifice providing a pressure signal for actuating said second control means.
 8. A medical respirator system, comprising in combination: a. a source of gas pressure; b. a bellows container having an inlet and a valved outlet controlled by a pressure chamber; c. a bellows having an inlet and an outlet mounted within said container, said bellows being expandable and collapsible between end positions; d. said source of fluid pressure being connected to said container through an interface valve and said pressure chamber; e. a breathing circuit for a patient serviced by said system being connected to the outlet of said bellows volume, said breathing circuit including exhaust valve means for venting said breathing circuit; f. control means for said breathing circuit exhaust valve; g. said valved outlet of said bellows container being connected to the inlet of said bellows; and h. fluid logic circuit means connected to said pressure source, to said control means for said breathing circuit exhaust valve, and to said interface valve; said circuit means being adapted to: (1) provide a first enabling signal for opening said interface valve to pressurize said chamber, thereby closing said container outlet valve and pressurizing said container to collapse said bellows forcing gas into said breathing circuit; (2) provide to said breathing circuit exhaust valve control means a second enabling signal simultaneous with said first enabling signal, for maintaining said breathing circuit exhaust valve closed; (3) terminate said first and second enabling signals to close said interface valve upon said bellows reaching its collapsed end condition, thereby removing pressure from said chamber and opening said outlet valve of said container enabling flow of gas from said container to said bellows inlet to expand said bellows, while opening said breathing circuit exhaust valve to relieve said breathing circuit pressure.
 9. A system in accordance with claim 8, including fluid switch means connected to said fluid logic circuit means, said switch means being operable upon said bellows reaching its collapsed end condition to provide a signal to said logic circuit for terminating said first and second enabling signals to said interface valve and breathing circuit exhaust valve control means.
 10. A system in accordance with claim 9, wherein said switch means includes a normally bled orifice, and a valve body displaceable to close said orifice, both said elements being mounted external to said container; said valve body including at least a first magnetic pole adjacent said container; and wherein the movable end of said bellows carries magnet means having a second pole opposite to the polarity of said first pole, movement of said bellows to said second position bringing said second pole toward said first pole to drive said valve body toward said orifice, thereby closing said orifice and providing said signal to said logic circuit.
 11. A system in accordance with claim 10, further including means coupling the pressure in said breathing circuit to an alarm input port at said fluid logic circuit, said logic circuit being adapted to provide at a first alarm output a first alarm signal upon the pressure at said breathing circuit dropping below a first predetermined level; and visual alarm indicator means connected to said first alarm signal to provide visual indication means connected to said first alarm signal to provide visual indication of said alarm condition.
 12. A system in accordance with claim 11, further including audible alarm indicator means coupled to said pressure source through a control valve means; said first alarm signal being coupled to said control valve whereby occurrence of said signal activates said control valve to enable said audible alarm.
 13. A system in accordance with claim 11, wherein said fluid logic circuit includes a second alarm output, timing means at said fluId logic circuit being adapted to provide a second alarm signal at said second output when the first enabling signal to said interface valve is present beyond a predetermined time period, said second signal being coupled to alarm indicators thereby signalling failure of cycling in said respirator system.
 14. A system according to claim 13, wherein said first and second alarm signals are both connected to a common alarm indicator.
 15. A system in accordance with claim 11, wherein the said fluid logic circuit is further adapted to terminate said first and second enabling signals upon the pressure from the said breathing circuit dropping below a second predetermined level, whereby said system is triggered between inhalation and exhalation phases in consequence of patient breathing effort.
 16. A system in accordance with claim 15, wherein said fluid logic circuit is adapted to provide a patient trigger signal upon said system being switched between said inhalation and exhalation phases by said patient effort, said signal being coupled to an observable alarm indicator means to indicate said patient triggered condition. 